Companies and governmental entities that employ mobile units often have difficulty locating the units. The units in turn often have difficulty knowing their position. In operations such as fighting forest fires or other types of wildfires, knowing the position of ground units is desirable to better manage the changing requirements for fighting the fire. A simple, reliable system for tracking assets and communicating back and forth therewith is thus desirable.
It is desirable to know both the location of the portable device and the base station and be able to communicate from a base station to a portable device. However, many devices include only one serial port. Both a GPS system and a wireless modem system should be connected to the serial port. One way in which to provide communications from a central microcontroller in the base station to both the GPS and a wireless modem is to provide an extra serial port. However, the extra serial port is prohibitively expensive. Using the parallel port for one of the devices is one option. This, however, would require a custom interface including a complex software driver to allow such communication.
It would therefore be desirable to provide a way in which to interface two devices to a single serial port without providing highly customized or expensive circuitry and drivers.